The Roast Game is pretty simple
First ask any family member "what is special about a holiday roast?"
The family member would have the tendency to guess assumptively
You say "no" to the family member
Then you ask them "who or what do you think is special?"
The family member says "I believe that children are special"
You respond "So, you eat children for a Christmas roast?"
The family member would freak out at you because he knew that the family ate children and he is surprised that you knew it too.
The whole point of the game is to get your point across, which is the idea that the family eats children as their Christmas roast, and you interview and prove your common knowing and realizing of the idea or tradition that families have.
If they freak out, they already admitted it.
Link to original debate: http://www.debate.org/debates/Bryan-Mullins-The-Roast-Game-Families-were-eating-their-own-children-for-19-years/1/